Deion Sanders says his estranged wife is straight up LYING … telling friends he NEVER offered her cash for sexual favors … and insists Pilar is simply trying to extort him for millions.

Sources close to Deion tell us the accusations are entirely untrue … and claim the NFL legend recently sent her a cashier’s check for $10,000 … which Pilar REJECTED.

Pilar’s lawyer, Larry Friedman, tells us she refused to accept the money because Deion presented the check as a “partial payment” towards the prenup … a prenup she believes is invalid.

We’re told Pilar was only promised $1,000,000 in the prenup … but Friedman believes she’s entitled to MILLIONS more … saying, “The offer does not reflect the assets in the estate and does not account for the time, effort, devotion, and faithfulness Pilar has invested in the marriage.”